The invention relates to stabilizer compositions as well as to a method for enhancing the light stability of polymers, in particular polyolefins.
It is the object of the present invention to provide an improved stabilizer composition for stabilizing polymers, in particular polyolefins, against the damage effected by light.
This object is achieved with the stabilizer composition as hereinunder described. It has surprisingly been found that masterbatch compositions of polyalkylpiperidines prepared in the presence of a free radical generator, exhibit an increased stabilization activity compared to the stabilization activity of masterbatch compositions according to the prior art which are produced without the addition of a free radical generator.
Accordingly, the present invention provides a light stabilizer composition obtainable by the process comprising the steps of
a) mixing a polymer with at least one polyalkylpiperidine and at least one free radical generator
b) melt-blending of that mixture at a temperature above the melting point of the polymer and above the decomposition temperature of the free radical generator and at shear conditions sufficient to blend the components.
The melt-blending temperature varies with the type of polymer and the type of the free radical generator. The skilled person can readily ascertain the appropriate temperature but a typical temperature range comprises the range from about 130xc2x0 C. to about 300xc2x0 C., preferably the range from about 150xc2x0 C. to about 230xc2x0 C.
The free radical generator is preferably a peroxide or hydroperoxide compound, in particular an organic peroxide compound. Suitable free radical generators are selected from the group consisting of dicumyl peroxide; 2,5-bis-tert.-butylperoxy-2,5-dimethylhexane; di-tert.-butyl-peroxide; isopropyl-tert.-butyl peroxy carbonate; bis-(tert.-butyl-2-peroxyisopropyl)-1,3-benzene; dimethyl-2,5-bis-(tert.-butylperoxy)-2,5-hexane; dimethyl-2,5-bis-(tert.-butylperoxy)-2,5-hexine-3; tert.-(butylcumyl peroxide, bis-(tert.-butyl)-3,3-ethyl butyrate.
The polyalkylpiperidine is an oligomeric or a high molecular-weight polyalkylpiperidine or a low molecular-weight polyalkylpiperidine or a polymer bound polyalkylpiperidine.
Preferably, the oligomeric or high molecular-weight polyalkylpiperidine is selected from the group consisting of compounds of formulae (I) to (VIII): 
poly-{[6-[(1,1,3,3-tetramethylbutyl)-imino]-1,3,5-triazine-2,4-diyl][2-(2,2,6,6-tetra-methyl-piperidyl)-amino]-hexamethylene-[4-(2,2,6,6-tetramethylpiperidyl)-imino]} (I)
[Commercially available for example as Chimassorb (registered trademark) 944 (Ciba Specialty Chemicals Inc.)]
1,3,5-triazine-2,4,6-triamine, N,Nxe2x80x2xe2x80x3-1,2-ethanediylbis[N-[3-[[4,6-bis[butyl(1,2,2,6,6-pentamethyl-4-piperidinyl)amino]-1,3,5-triazin-2-yl]methylamino]propyl]-Nxe2x80x2,Nxe2x80x3-dibutyl-Nxe2x80x2,Nxe2x80x3-bis-(1,2,2,6,6-pentamethyl-4-piperidinyl)- (II)
[Commercially available for example as Chimassorb (registered trademark) 119 ((Ciba Specialty Chemicals Inc.)]
poly[(6-morpholino-s-triazine-2,4-diyl)[2,2,6,6-tetramethyl-4-piperidyl)-imino]-hexamethylene[(2,2,6,6-tetramethyl-4-piperidyl)imino] (III)
[Commercially available for example as Cyasorb (registered trademark) UV 3346 (American Cyanamid Inc.)]
poly-(N-xcex2-hydroxyethyl-2,2,6,6-tetramethyl-4-hydroxy-piperidyl-succinate) (VI)
[commercially available for example as Tinuvin (registered trademark) 622 (Ciba Specialty Chemicals Inc.). 
polymethylpropyl-3-oxy-[4(2,2,6,6 tetramethyl)-piperidinyl]-siloxane (V)
[Commercially available for example as Uvasil (registered trademark) 299 (Great Lakes Chemical Corp.)]
Oligomer obtained by the reaction and subsequent oligomerization of 2,2,4,4-tetramethyl-21-oxo-7-oxa-3,20-diazadispiro-[5.1.11.2]-heneico (VI) sane or its hydrochloride with epichlorohydrine.
[Commercially available for example as Hostavin (registered trademark) N-30 (Hoechst)]
1,3-propanediamine, N,Nxe2x80x3-1,2xe2x80x2-ethanediyl-bis-, polymer with N-butyl-2,2,6,6-tetramethyl-4-piperidinamine and 2,4,6-trichloro-1,3,5-triazine (VII)
[commercially available for example as Uvasorb (registered trademark) HA-88]
poly-[3-eicosyl(-tetracosyl)-1-(2,2,6,6-tetramethylpiperidine-4-yl)-pyrrolidine-2,5-dione] (VIII)
[commercially available for example as Uvinul 5050 H]
Preferably, the low molecular-weight polyalkylpiperidine is selected from the group consisting of compounds of formulae (IX) to (XIII) 
bis-2,2,6,6-tetramethyl-4-piperidyl-sebacate (IX)
[commercially available for example as Tinuvin (registered trademark) 770 (Ciba Specialty Chemicals Inc.)]
propanedioic acid, [(4-methoxyphenyl)-methylene]-bis(1,2,2,6,6-pentamethyl-4-piperidinyl)-ester] (X)
[Commercially available for example as Sanduvor (registered trademark) PR 31 (Clariant)]
a mixture of esters of 2,2,6,6-tetramethyl-4-piperidinol and higher fatty acids (mainly stearic acid) (XI)
[commercially available for example as Dastib (registered trademark) 845 or Cyasorb (registered trademark) UV 3853]
2,2,6,6-tetramethyl-21-oxo-7-oxa-3,20-diazadispiro[5.1.11.2]-heneicosane (XII)
[commercially available for example as Hostavin (registered trademark) N-20 (Hoechst)]
2,2,4,4-tetramethyl-21-oxo-7-oxa-3,20-diazadispiro[5.1.11.2]-heneicosan-20-propanoic-acid-dodecyles (XIII)
[commercially available for example as Hostavin (registered trademark) N-24 (Hoechst)].
The polyalkylpiperidine is typically used in an amount of from 0.1 to 70% by weight, preferably from 5 to 30% by weight based on the weight of the polymeric composition.
Typical quantities of the free radical generator is from 0.01 to 10% by weight, preferably from 0.1 to 2% by weight based on the weight of the polymeric composition.
All compounds of formulae (I) to (XIII) are known or may be made from known compounds by known methods.
The polymer of the stabilizer composition according to the invention is a thermoplastic organic polymer, preferably selected from polyolefins and copolymers and blends thereof.
Further additives, which may be added, if appropriate, include antioxidants, UV-absorbers, pigments, dyes, nucleating agents, fillers, and property modifiers and several others commonly used.
A further object of the invention is a method for enhancing the light stability, preferably UV light stability, of polymeric materials, preferably thermoplastic organic polymers, which are identical or compatible with the polymer component of the stabilizer composition according to the invention. This method comprises incorporating before or during processing a stabilizing quantity of the stabilizing composition according to the invention into the polymeric material to be stabilized. The quantity of the light stabilizer composition according to the invention needed to confer an appreciable extent of stabilization varies with the amount of the polyalkylpiperidine compound as well as with the type of the polymer and the end use of the finished article. The skilled person can readily ascertain the appropriate quantity for the diverse fields of applications.

The invention is further illustrated by means of the following examples in which all parts are expressed by weight.